Greater Charge Density Research Articles

Desorption behavior and mechanism of yttrium ions from ion-adsorption type rare earths ore

Ion-adsorption type rare earths ore (IREO) is an important strategic resource that can be leached in-situ using electrolytes such as NH4+, Mg2+, and Al3+. However, the use of NH4+ was restricted due to ammonia-nitrogen pollution, regarding in-situ leaching agents still remain controversial. It is imperative to comprehensively and systematically investigate the desorption mechanism of rare earth elements (REEs) from a microscopic perspective, especially when using Mg2+ and Al3+ as leaching agents. In this manuscript, the desorption behavior and mechanism of Y3+ from ADY (IREO as adsorbents loaded with Y3+) were studied, along with a comparison of the Y3+ desorption capabilities of Mg2+ and Al3+ as leaching agents. The results showed that Y3+ could be effectively desorbed from IREO by both Mg2+ and Al3+, with Y3+ desorption yields of 93.1 % (pH 3.2, 0.06 mol/L) for Al3+ and 88.6 % (pH 6.0, 0.3 mol/L) for Mg2+, respectively. The superior Y3+ desorption capability of Al3+ arises from its higher valence, greater electronegativity, and smaller ionic radius compared to Mg2+. The higher valence imparts Al3+ greater charge density, while the greater electronegativity enables Al3+ to more readily substitute for Y3+. Additionally, the smaller ionic radius facilitates the entry of Al3+ into clay minerals interlayers. At high H+ concentrations, the Y3+ desorption capabilities of Mg2+ and Al3+ were both higher than at the original pH without acid addition, primarily due to the influence of H+, which could leach Y3+ from the un-exchangeable phase, but also significantly increased the leaching of impurities. The isotherms and kinetics demonstrated the desorption of Y3+ in the case of Mg2+ and Al3+ existing followed the Langmuir and pseudo-second-order models, indicating homogeneous, chemisorption-governed processes. Furthermore, ATR-FTIR, XPS, and DFT results revealed Y3+ desorption occurred by breaking SiOY bonds and ion exchange with Mg2+/Al3+ to form SiOMg/Al bonds.

Complex Materials with Stochastic Structural Patterns: Spiky Colloids with Enhanced Charge Storage Capacity.

Self-assembled materials with complex nanoscale and mesoscale architectureattract considerable attention in energy and sustainability technologies. Their high performance can be attributed to high surface area, quantum effects, and hierarchical organization. Delineation of these contributions is, however, difficult because complex materials display stochastic structural patterns combining both order and disorder, which is difficult to be consistently reproduced yet being important for materials' functionality. Their compositional variability make systematic studies even harder. Here, a model system of FeSe2 "hedgehog" particles (HPs) was selected to gain insight into the mechanisms of charge storage n complex nanostructured materials common for batteries and supercapacitors. Specifically, HPs represent self-assembled biomimetic nanomaterials with a medium level of complexity; they display an organizational pattern of spiky colloids with considerable disorder yet non-random; this patternt is consistently reproduced from particle to particle. . It was found that HPs can accommodate ≈70× greater charge density than spheroidal nano- and microparticles. Besides expanded surface area, the enhanced charge storage capacity was enabled by improved hole transport and reversible atomic conformations of FeSe2 layers in the blade-like spikes associated with the rotatory motion of the Se atoms around Fe center. The dispersibility of HPs also enables their easy integration into energy storage devices. HPs quadruple stored electrochemical energy and double the storage modulus of structural supercapacitors.

Isostructural Series of Ni(II), Pd(II), Pt(II), and Au(III) Azido Complexes with a N^C^N Pincer Ligand to Elucidate Trends in the iClick Reaction Kinetics and Structural Parameters of the Triazolato Products.

An isoelectronic and isostructural series of cyclometalated azido complexes [M(N3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) based on the N^C^N pincer ligand 1,3-di(2-pyridyl)phenide (dpb) was characterized by X-ray diffraction analysis and investigated for reactivity in the iClick reaction with a wide range of internal and terminal alkynes by using 1H and 19F NMR spectroscopy. Reaction rate constants were found to increase with greater charge density in the order Ni(II) > Pd(II) > Pt(II) > Au(III). Terminal alkynes R-C≡C-R' with strongly electron-withdrawing groups R and R' exhibited faster kinetics than those with electron-donating substituents in the order CF3 > ketone > ester > H > phenyl ≫ amide, while R = CH3 resulted in complete loss of reactivity. Four symmetrical triazolato complexes [M(triazolatoCOOCH3,COOCH3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) as well as four nonsymmetrically substituted triazolato complexes [Pt(triazolatoR,R')(dpb)] originating from terminal and internal alkynes were shown by X-ray crystal structure analysis to exclusively feature N2-coordination of the five-membered ring ligand. However, the Pt(II) triazolato complexes exist as a mixture of N1- and N2-coordinated species in solution. Torsion angles between the mean planes of the N^C^N pincer and the triazolato ligand increase from a nearly coplanar to a perpendicular arrangement when going from Au(III)/Pt(II)/Pd(II) to Ni(II), while different substituents R and R' on the alkyne have no influence on the torsion angle and were rationalized by DFT calculations. Finally, a carbohydrate derivative obtained by glucuronic acid conjugation to methyl propiolate demonstrates the facile biofunctionalization of metal complexes via the iClick reaction.

Upgrading the Hydrogen Storage of MOF-5 by Post-Synthetic Exchange with Divalent Metal Ions

In metal-organic frameworks (MOFs), mixed-metal clusters have the opportunity to adsorb hydrogen molecules due to a greater charge density of the metal. Such interactions may subsequently enhance the gravimetric uptake of hydrogen. However, only a few papers have explored the ability of mixed-metal MOFs to increase hydrogen uptake. The present work reveals the preparation of mixed metal metal-organic frameworks M-MOF-5 (where M = Ni2+, Co2+, and Fe2+) (where MOF-5 designates MOFs such as Zn2+ and 1,4-benzenedicarboxylic acid ligand) using the post-synthetic exchange (PSE) technique. Powder X-ray diffraction patterns and scanning electron microscopy images indicate the presence of crystalline phases after metal exchange, and the inductively coupled plasma–mass spectroscopy analysis confirmed the exchange of metals by means of the PSE technique. The nitrogen adsorption isotherms established the production of microporous M-MOF-5. Although the additional metal ions decreased the surface area, the exchanged materials displayed unique features in the gravimetric uptake of hydrogen. The parent MOF-5 and the metal exchanged materials (Ni-MOF-5, Co-MOF-5, and Fe-MOF-5) demonstrated hydrogen capacities of 1.46, 1.53, 1.53, and 0.99 wt.%, respectively. The metal-exchanged Ni-MOF-5 and Co-MOF-5 revealed slightly higher H2 uptake in comparison with MOF-5; however, the Fe-MOF-5 showed a decrease in uptake due to partial discrete complex formation (discrete complexes with one or more metal ions) with less crystalline nature. The Sips model was found to be excellent in describing the H2 adsorption isotherms with a correlation coefficient ≅ 1. The unique hydrogen uptakes of Ni− and Co-MOF-5 shown in this study pave the way for further improvement in hydrogen uptake.

In-situ synthesis of an integrated CuN3/CL-20 explosive train film with excellent initiation ability

In-situ construction of energetics-on-a-chip by the microcharge technique has recently received much attention by researchers. In this study, a novel integrated CuN3/CL-20 explosive train film was fabricated in-situ on a Cu substrate. The porous CuN3 film, which was synthesized by facile electrochemical azidation of porous Cu, served as a skeleton for the integration of CL-20 by means of spin-coating and recrystallization. In this architecture, the introduction of CL-20 endowed the resultant explosive train film with a greater charge density and an enhanced energy output than a single CuN3 film. In particular, the tunability of exothermic capacity could be controlled by adjusting the loading amount of CL-20. Additionally, the embedded CL-20 and CuN3 film jointly ensured violent explosive behavior upon laser stimulation. Given these advantages, this CuN3/CL-20 explosive train film exhibits great potential for application in functional energetic chips.

Intercalation of Solvated Magnesium-Ions into Layered Transition Metal Sulfide for Fast Mg Storage

Rechargeable magnesium (Mg) batteries (RMBs) are potential candidates for new generation battery technologies due to the attractive properties of Mg as a metal anode, especially the intrinsic nature of homogeneous Mg deposition and abundant Mg reserves. Compared to the monovalent counterpart (e.g. Li+), the divalent Mg ions have a greater charge density and thus need to overcome much stronger electrostatic forces for insertion and diffusion inside the host structures. One of the strategies to enhance Mg2+ ion intercalation kinetics is to reduce its charge density. Herein, we present the intercalation chemistry of the solvated ions [Mg(DME)3]2+, in which the improved ion mobility has been proven by various electrochemical and spectroscopic characterizations.1 The novel concept was realized with Mg[B(hfip)4]2/DME electrolyte2, 3 and a layered MoS2 cathode coupled with a Mg anode. The cell configuration exhibited a long-term cycling stability (>200 cycles) and high rate capability (47 mA h g-1 at 0.5 A g-1). In addition, the mechanism of Mg storage has been investigated in detail, revealing the reversible 2H to 1T MoS2 phase transition during Mg ions de-/intercalation. Compared to other reported intercalation with [Mg(H2O)x]2+ or MgCl-,4, 5 the DME molecules will neither passivate the anode nor corrode the cell components, which makes this approach more practical. Moreover, the concept of solvated Mg2+ ions can be potentially extended to other intercalation cathode materials and applied to other multivalent ions intercalation. References Z. Li, X. Mu, Z. Zhao-Karger, T. Diemant, R. J. Behm, C. Kübel and M. Fichtner, Nature Communications, 2018, 9, 5115.Z. Zhao-Karger, M. E. Gil Bardaji, O. Fuhr and M. Fichtner, J. Mater. Chem. A, 2017, 5, 10815-10820.Z. Zhao-Karger, R. Liu, W. Dai, Z. Li, T. Diemant, B. P. Vinayan, C. Bonatto Minella, X. Yu, A. Manthiram, R. J. Behm, M. Ruben and M. Fichtner, ACS Energy Letters, 2018, 3, 2005-2013.K. W. Nam, S. Kim, S. Lee, M. Salama, I. Shterenberg, Y. Gofer, J.-S. Kim, E. Yang, C. S. Park, J.-S. Kim, S.-S. Lee, W.-S. Chang, S.-G. Doo, Y. N. Jo, Y. Jung, D. Aurbach and J. W. Choi, Nano Letters, 2015, 15, 4071-4079.H. D. Yoo, Y. Liang, H. Dong, J. Lin, H. Wang, Y. Liu, L. Ma, T. Wu, Y. Li, Q. Ru, Y. Jing, Q. An, W. Zhou, J. Guo, J. Lu, S. T. Pantelides, X. Qian and Y. Yao, Nature Communications, 2017, 8, 339.

Thiocyanate-Ligated Heterobimetallic {PtM} Lantern Complexes Including a Ferromagnetically Coupled 1D Coordination Polymer.

A series of heterobimetallic lantern complexes with the central unit {PtM(SAc)4(NCS)} have been prepared and thoroughly characterized. The {Na(15C5)}[PtM(SAc)4(NCS)] series, 1 (Co), 2 (Ni), 3 (Zn), are discrete compounds in the solid state, whereas the {Na(12C4)2)}[PtM(SAc)4(NCS)] series, 4 (Co), 5 (Ni), 6 (Zn), and 7 (Mn), are ion-separated species. Compound 7 is the first {PtMn} lantern of any bridging ligand (carboxylate, amide, etc.). Monomeric 1-7 have M(2+), necessitating counter cations that have been prepared as {(15C5)Na}(+) and {(12C4)2Na}(+) variants, none of which form extended structures. In contrast, neutral [PtCr(tba)4(NCS)]∞ 8 forms a coordination polymer of {PtCr}(+) units linked by (NCS)(-) in a zigzag chain. All eight compounds have been thoroughly characterized and analyzed in comparison to a previously reported family of compounds. Crystal structures are presented for compounds 1-6 and 8, and solution magnetic susceptibility measurements are presented for compounds 1, 2, 4, 5, and 7. Further structural analysis of dimerized {PtM} units reinforces the empirical observation that greater charge density along the Pt-M vector leads to more Pt···Pt interactions in the solid state. Four structural classes, one new, of {MPt}···{PtM} units are presented. Solid state magnetic characterization of 8 reveals a ferromagnetic interaction in the {PtCr(NCS)} chain between the Cr centers of J/kB = 1.7(4) K.

Spermine Sepharose as a clustered-charge anion exchange adsorbent

We previously showed that the affinity and capacity of ion exchange adsorbents of a given total charge density are improved by immobilization of the charges in pre-ordered clusters, rather than individually in random locations. This previous work used pentalysinamide and pentaargininamide as clustered ligands. This approach allows close control of cluster size, but is uneconomically expensive for some research and most practical applications. In this work, we demonstrate that the inexpensive synthetic analog of the natural polyamine spermine (H2NCH2CH2CH2NHCH2CH2CH2CH2NHCH2CH2CH2NH2) also can serve as the basis of effective clustered adsorbents. The calcium-depleted form of the protein α-lactalbumin, and RNA from baker's yeast, were adsorbed on a spermine Sepharose adsorbent. This adsorbent exhibited enhanced α-lactalbumin binding capacity (Qmax>1.6 and 1.3-fold higher than those for Qiagen DEAE and GE DEAE Sepharose adsorbents of much greater charge density) and higher initial binding affinity (Qmax/KD 2.4 and 2.1-fold higher, respectively). The new spermine-based matrix exhibited a higher value of the Z parameter, suggesting an increased number of apparent interaction sites between the protein and the resin, and functioned well in column mode.

Odor-active compound adsorption onto bentonite in a model white wine solution.

This work extends the concepts proposed in a previous research paper about the interaction between the aroma of two white wines and bentonites. Such previous results led to hypothesized that some odor-active compounds were removed through direct adsorption mechanism on the clays. As a consequence, this paper examined the adsorption isotherms at 17±1°C of three bentonite samples added in three different amounts to a model white wine without the presence of wine macromolecule. The clays were analyzed for the elemental composition, the surface charge density, and the specific surface area (SSA) and differences were analyzed by Tukey’s test. The analysis of variance (ANOVA) was used to demonstrate the significance of the bentonite on the aroma reduction. The Langmuir and the Freundlich models were fitted to the adsorption data. The most experimental adsorption isotherms were robustly fitted by the Freundlich equation indicating that, under the condition of the study, the adsorption process more frequently occurred with a heterogeneous energy distribution of an infinite number of surface active sites. Overall, the modeling prediction ability tested by the error on r 2 in cross validation enhanced differences both among the odor-active compounds and among the clays. Samples having a lower SSA value and a greater charge density per surface unit seemed to interact with most of the odor-active compounds primarily through physical mechanisms. Differently, the clay with a large SSA value and a low charge density per surface unit promoted stronger adsorptions that were probably driven by chemical interactions especially for ethyl esters. For the tested odor-active compounds differences in the adsorption intensity and capacity depended mainly on the bentonite characteristics rather than on the properties of the substances.

Reduction of electrode polarization capacitance in low-frequency impedance spectroscopy by using mesh electrodes

Dielectric measurements of biological samples are obscured by electrode polarization, which at low frequencies dominates over the actual sample response. Reduction of this artifact is especially necessary in studying interactions of electric field with biological systems in the α-dispersion range. We developed a method to reduce the influence of electrode polarization by employing mesh instead of solid electrodes as sensing probes, thereby reducing the area of the double layer. The design decreases the electrode–electrolyte contact area by almost 40% while keeping the bulk sample capacitance the same. Interrogation electric fields away from the electrode surface and sensitivity are unaffected. Electrodes were microfabricated (600μm×50μm, spacing of 100μm) with and without mesh holes 7.5μm×7.5μm in size. Simulations of electric field performed using Comsol Multiphysics showed non-uniformity of the electric field within less than 1.5μm from the electrode surface, which encompasses the double layer region, but at greater distance the solid and mesh electrodes gave the same results. Mesh electrodes reduced capacitance measurements for water and KCl solutions of different concentrations at low frequencies (<10kHz), while higher frequency capacitance remained the same for both electrode types, confirming our hypothesis that this design leaves the electric field mainly unaffected. Impedance measurements at low frequencies for water and mice heart mitochondrial suspension were lower for mesh than for solid electrodes. Comsol simulations confirmed these results by showing that mesh electrodes have a greater charge density than solid electrodes, which affects conductance. These electrodes are being used for mitochondrial membrane potential studies.

Low-spin complexes of Ni 2+ with six NH 3 and H 2O ligands: A DFT–RX3LYP study

The gas-phase energy minimization of six-coordinate Ni 2+ octahedral structures ( S = 1) with H 2O and NH 3 using the DFT/RX3LYP/6-311++G(d,p) level of theory and S = 0 leads to the formation of square planar complexes of the type [Ni(NH 3) n(H 2O) m] 2+·sH 2O·(2 − s)NH 3, n + m = 4, 0 ≤ n, m ≤ 4, 0 ≤ s ≤ 2. The H-bonding between inner- and outer-sphere (IS and OS) ligands results in the formation of six-member rings characterized by ring critical points. If OS H 2O, H-bonded to IS H 2O, is changed to NH 3, it deprotonates the latter with hydroxide strongly H-bonded to OS NH 4 +, a phenomenon not observed in the modeling of equivalent complexes of Zn 2+ and Cu 2+. The four-coordinate hexa complexes are found to be over 50 kcal mol −1 more stable than the equivalent octahedral structures; this is twice as large as reported for Cu 2+, and much larger than for Zn 2+ complexes. The stability of complexes with two OS H 2O increases by 13 kcal mol −1 as IS H 2O is replaced by NH 3; this is twice as much as found for the analogous octahedral complexes. The deprotonation of IS H 2O by OS NH 3 leads to a stabilization by 10 kcal mol −1; interchanging IS H 2O with OS NH 3 increases stability by a further 4–8 kcal mol −1. The increased stability of these four-coordinate hexa complexes is associated with greater charge density ρ bcp at the bond critical points of Ni O and Ni N bonds and a greater charge transfer to the metal (0.708–1.067 e).

Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl 2), bromine (Br 2) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene ( 1) and 1,3-butadiene ( 2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl 2 and Br 2 with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.

The greater negative charge density of DNA in Tris‐borate buffers does not enhance DNA condensation by multivalent cations

The greater negative charge density of DNA in Tris‐borate buffers does not enhance DNA condensation by multivalent cations

Fundamental factors controlling the exchange of multidentate ligands: displacement of 12-crown-4 and triglyme from complexes with divalent alkaline earth cations

In an effort to shed light on the factors that influence the recognition of alkaline earth cations in natural systems, we have studied intrinsic recognition of these cations by well-ordered synthetic ionophores such as crown ethers (12-crown-4 [C4] and 18-crown-6 [C6]) as well as the acyclic analog of C4, triglyme (TG), in the gas phase. We have employed electrospray ionization (ESI) to generate gas phase crown and glyme alkaline earth complexes, and have used Fourier transform ion cyclotron resonance mass spectrometry to measure rate constants for displacement of the original ligands by C6. ESI of mixtures of C4 and TG with alkaline earths primarily produces sandwich complexes of the doubly charged cations, (C4) 2M 2+, (C4)(TG)M 2+, and (TG) 2M 2+. We find that the ligand exchange reactions are generally very efficient, with rates approaching or exceeding the Langevin collision rate in most cases. Trends in rates as metal size varies can be understood in terms of the degree of encapsulation of the metal by the ligands when the coordination shell is partially filled (smaller metals are more thoroughly encapsulated and tend to react more slowly) and in terms of the polarizing power of the metal cation when the metals are either “bare” or completely coordinated (smaller metals have greater charge density and tend to react more rapidly). Efficiencies for most of the reactions studied fall off in the order Mg 2+ > Ca 2+ > Sr 2+ > Ba 2+, consistent with decreasing charge density as the cation radius increases. Interestingly, TG is displaced more efficiently than C4 by C6, despite the fact that the total binding energy of the glyme is greater than that of the crown. This is consistent with a mechanism wherein the rate-limiting step involves breaking O–M 2+ electrostatic bonds, and where the bonds to the oxygens of TG can be broken one at a time, whereas the more rigid ring structure of C4 requires concerted breaking of multiple bonds. Molecular dynamics simulations of this process for complexes where M 2+ = Ca 2+ give support to this interpretation: in all observed dissociation events, TG oxygens were removed from the metal one at a time, whereas displacement of C4 oxygens occurred in pairs.

Interaction of the chloropentaamminecobalt(III) cation with dihexadecylphosphate vesicles in the absence and the presence of poly(propylene glycol). A kinetic study

The electrostatic interaction between the cationic chloropentaamminecobalt(III) complex and the exterior anionic surface of sodium dihexadecylphosphate (DHP) vesicles in the absence and the presence of varying amounts of the polymer PPG-425 [poly(propylene glycol) with Mw=425] has been studied at 25.0°C by examining the vesicular retarding effects on the kinetics of the alkaline hydrolysis of the cobalt(III) complex. The kinetic data indicate that two reaction paths contribute to the overall hydrolysis rate. In the absence of polymer the interactions involving the cobalt complex, as deduced from the estimated binding constant (KA), are markedly larger than those found previously with anionic micelles of sodium dodecyl sulfate (SDS). Moreover, the rate constant (kv″) for the pathway involving the hydroxide ion in the outer aqueous vesicular compartment and the complex solubilized in the exterior vesicle surface is smaller than the corresponding rate constant obtained with SDS micelles. These results suggest the existence of greater charge density at the DHP vesicular surface. In the presence of polymer both KA and kv″ parameters remain substantially unchanged up to the polymer content of 0.30%, but the binding constant undergoes a decrease and the rate constant kv″ an increase at higher polymer concentration. These findings are primarily attributed to the decrease in the charge density of the external vesicular surface induced by the polymer penetration.

The effect of pH on polymerization and volume change in PPy(DBS)

Polymerization and electrochemically induced volume change in polypyrrole doped with the large aromatic surfactant anion dodecylbenzenesulfonate, PPy(DBS), were studied as a function of pH in unbuffered aqueous solutions prepared by mixing DBS acid and NaOH. Volume change was measured during the first, anomalous reduction and in subsequent cycles using a bending bilayer. The results differed completely from those obtained by others for PPy doped with small, mobile anions. Films could be deposited potentiostatically at all nominal pH values between 1 and 11, but growth was fastest at the lowest pH and uneven above pH 10 due to impaired nucleation. However, during potentiodynamic polymerization, deposition and redox were easier at alkaline pH, having a smaller peak separation and greater charge density. At pH less than 3, there were no reduction or oxidation (redox) peaks and the films became insulating. Contrary to expectations, the pH of the growth solution did not affect the performance of the bilayer actuators, but the pH of the cycling solution was important. Bending was fastest in alkaline solutions, although the degree of bending was the same at low and high pH. Except at very low pH, two pairs of redox peaks could be distinguished in the cyclic voltammograms, with volume change restricted to the lower potential pair associated with Na + movement. There was no volume change associated with the anomalous current peak seen during the first reduction scan, regardless of pH, but the films contracted during re-oxidation. Thereafter, during reduction the films expanded to their original, as-grown volume.

Bile acid measurements using a cholestyramine-coated TSM acoustic wave sensor.

A novel chemical sensor for bile acids is described. A 10-MHz piezoelectric crystal operating in the thickness-shear mode (TSM) is coated on one side with cholestyramine resin and mounted in a batch-mode sensor block which exposes the coating to solution. After sample injection, the binding process is observed in real time as a drop in frequency as the bile salt binds to the coating, reaching > 90% completion within 10 min with most of the binding occurring within the first minute. Linear calibration curves are generated with sensitivity increasing in the order cholate approximately glycocholate < taurocholate < < taurodeoxycholate. Detection limits in water are in the range 0.2-9 nmol and are better than those observed in phosphate buffer. A multistep regeneration protocol allows the coating to be reused more than 400 times over a period of several months. Precision for replicate injections is approximately 10% RSD and depends on the reproducibility of the regeneration and injection steps. In terms of the binding process, hydrophobic interactions are observed to be of importance in the ability of bile salts to displace other counterions. However, anions with greater charge density also appear to compete effectively for binding sites on the resin. In particular, at equimolar concentrations of citrate and bile salt, the trivalent citrate anion reduces the amount of bile salt binding by approximately 40%. This suggests that the efficiency of cholestyramine-based bile salt sequestering drugs used in the reduction of hypercholesterolemia may be improved by eliminating citric acid as an excipient and avoiding the use of fruit juices during ingestion.

Spectral Studies of Lanthanide Interactions with Membrane Surfaces

We have monitored the interactions of the series of trivalent lanthanide cations with the thylakoid membrane surface of spinach chloroplasts using two complementary spectral techniques. Measurements of the fluorescence emission of the extrinsic probe 2-p-toluidinonaphthalene-6-sulfonate (TNS) and the absorbance of the intrinsic chromophore chlorophyll provide two sensitive means of characterizing the dependence of the cation-membrane interaction on the nature of the cation. In these systems, added lanthanide cations adsorb onto the membrane surface to neutralize exposed segments of membrane-embedded protein complexes. The lanthanide-induced charge neutralization increases the proximity of added TNS anion to the membrane surface as evidenced by variations in the TNS fluorescence level and wavelength of maximum emission. Our results reveal a strong dependence of TNS fluorescence parameters on both lanthanide size and total orbital angular momentum L value. Lanthanides with greater charge density (small size and/or low L value) enhance the TNS fluorescence level to a greater extent. A possible origin for the lanthanide-dependent TNS fluorescence levels is suggested in terms of a heterogeneity in the number and type of TNS binding sites. The data are consistent with the proposal that larger lanthanides with smaller enthalpies of hydration induce more significant membrane appression. 59 refs., 9 figs.,more » 2 tabs.« less

Acidic Biopolymers as Dispersants for Ceramic Processing

AbstractSome acidic biopolymers serve as dispersants for colloidal processing of ceramics. One biopolymer we tested was alginate, a heteropolysaccharide containing two carboxylic sugar acids, D-mannuronic and D-guluronic. Kelp alginate was a suitable dispersant, provided that its viscosity was reduced by partial acid hydrolysis. Low molecular weight polymers rich in guluronic acid proved to be better dispersants than those rich in mannuronic acid, perhaps due to their greater charge density caused by their buckled molecular configuration. In situ processing of ceramic materials was tested by growing the alginate-producing bacterium, Azotobacter vinelandii, in the presence of alumina particles. Growth occurred at 15 vol% alumina in medium. Alumina particles which were exposed to such treatment showed a high packing density comparable to that with purified polymer. We also tested polypeptide polymers of the dicarboxylic amino acids, glutamate and aspartate, which also served as excellent dispersants for small alumina particles.

A comparison of the proteoglycans synthesized in Meckel's and sternal cartilage from normal and nanomelic chick embryos

Proteoglycan synthesis in Meckel's cartilage, a mesectodermal derivative of neural crest origin, is analyzed in normal and mutant nanomelic chick embryos.In vitro synthesis of chondroitin sulfate by Meckel's cartilage chondrocytes from mutant embryos is 12% of normal levels. Molecular sieve chromatography and sucrose gradient analysis of proteoglycans show that this decrease in chondroitin sulfate synthesis is limited to that fraction of molecules which is specific for cartilaginous tissues. The sedimentation rate of the proteoglycan monomer from normal Meckel's cartilage is slightly greater than that from normal sternal cartilage. The glycosaminoglycans from the normal Meckel's monomer have a greater charge density than those from normal sternal monomer. Both Meckel's and sternal proteoglycans from normal embryos can be aggregated with hyaluronic acid and probably represent a class of cartilage-specific proteoglycans which are genetically distinct from a slower sedimenting population of proteoglycans found in fibroblastic type cells. It appears from the analysis on sternal nanomelic cartilage that these chondrocytes are capable of synthesizing small amounts of the cartilage-specific proteoglycans.